A violent tornado raged for six seconds through a Mexican city along the U.S. border on Monday, killing at least 13 people and flattening hundreds of homes.

The 250-kilometer-an-hour twister hit Ciudad Acuna at dawn, flinging cars and big-rig trucks into the air and smashing them into houses and buildings in a seven-block area. Rescue workers were searching for survivors in 750 damaged properties.

To the north, in the U.S. state of Texas, searchers continued to look for 12 people believed to have been swept away in flash flooding. The flooding was spawned by a line of storms that stretched from the Gulf of Mexico far northward to the Great Lakes as they swept across the United States.

Already, the flooding has left three people dead and destroyed at least 400 homes in Texas and the neighboring state to the north, Oklahoma.

Texas Governor Greg Abbott declared an emergency in 24 of the state's counties in addition to 13 others he had named previously.

More than 2,000 people in Texas were forced to evacuate their homes Sunday and Monday.

The storm spawned a tornado in Texas. Cars and trucks were submerged in the Texas city of San Marcos, with the Blanco River reaching levels not seen in nearly a century.

Some San Marcos residents escaped their homes by floating down flooded streets in inflatable lounge chairs. The city opened emergency shelters to house the flood victims.